1. Field of the Invention
The present invention relates to a magnetic disk memory which has a hub seated at both sides of a magnetic disk with the assistance of a shaft, carrying at least one storage disk and driven by a motor, whereby a pair of ball bearings is provided for bearing the hub in mutually opposite walls of a housing, the ball bearings being restrained in the axial direction relative to one another in order to achieve a play-free hub guidance.
2. Description of the Prior Art
A distinction is generally made in magnetic disk memories between memories having fixed disk packs and exchangeable disk packs. Technical development is continuing to proceed in the direction of higher and higher storage capacities, both in view of the track density and the bit density as the characteristic for the storage capacity per disk surface, on the one hand, and in view of the mechanical structure in order to be able to accommodate as many magnetic disks as possible in a prescribed mounting space. An example of this is the so-called 51/4" fixed disk memory whose magnetic disks have an outer diameter of 130 mm and an inside diameter of 40 mm according to, for example, the German industrial standard. Analogous to the dimensions of competing flopping disk drives, a mounting space having a mounting height of 82.5 mm and a base area of 146 mm.times.203 mm has crystallized out of this type of storage as a uniform size which is available for the overall apparatus including a housing and the appertaining electronics.
The desire to accommodate as many magnetic disks as possible in this prescribed mounting space is subordinate to the developmental goal of higher storage capacities and to the efforts to increase the recording density on the magnetic disks. Within the scope of this structural endeavor, embodiments of 51/4" fixed disk memories have been disclosed wherein the drive motor for the disk pack has been miniaturized to such a degree and has been structurally designed such that it can still be built into the hub of the disk pack, even given a prescribed inner diameter of 40 mm for the disk packs. An element which has a significant co-determining effect on the overall height of conventional fixed disk memories is therefore integrated in the hub of the magnetic disk pack and the overall height exploitable for the disk stack is therefore expanded. Based on current considerations in the size of the combined magnetic heads and of the disk thickness, disk packs which contain up to eight magnetic disks stacked on top of one another have therefore become possible. The remaining overall height is required for the housing and the drive electronics.
As mentioned above, the recording density on the magnetic disk is the product of the write density times the track density. A significant criterion for the structural format of a magnetic disk memory also occurs for the case of the present invention, specifically from the track density having, for example, more than 1000 tracks/inch. This high track density requires the best possible vibration-isolated seating of the spindle of the disk pack in the housing. Requirements are therefore made for this type of storage such as heretofore played a part only with respect to large and expensive disk memories, for example the 14" disk memories.
For such high capacity disk memories having a larger diameter, it is generally known to seat the spindle of the disk pack at one side in a heavy base plate, in part in structures designed in a very involved manner, this particularly applying to conventional memories having exchangeable disk packs, i.e. memory designs which allow for removing the disk pack from the magnetic storage device. On the other hand, structures are also known wherein the spindle is seated at both sides in a rigid housing surrounding the pack. In order to achieve as vibration-isolated a spindle seating as possible, a fixed bearing and a movable bearing are employed given this two-sided seating and a spring is provided adjacent the movable bearing, the spring tensing the two bearings relative to one another after assembly such that a coaxial spindle guiding that is as free of play as possible is achieved. However, this goal can only be achieved to an extent limited by the inherent characteristics of such a combination of fixed and movable bearings. Further, additional mounting space is required for the incorporation of the spring, this therefore being lost as useable storage space on the one hand, and taking away valuable space when the motor is built into the hub, on the other hand.